The present invention relates to a multilayer optical disk having a multilayer structure consisting of a plurality of layers for storing information.
In recent years, the popularity of so-called multimedia results in a necessity of handling large-capacity information such as a digital movie data. Therefore, a necessity arises in that large-capacity information of the foregoing type must be stored and randomly accessed so as to be reproduced, if need arises.
An optical disk is a storage medium permitting random access, exhibiting a large capacity and capable of being ejected (i.e., being removable) from a playback or reproducing apparatus. Therefore, optical disks have been used in a variety of fields and large quantities. In order to enlarge the capacity as described above, one side of the optical disk must be capable of handling large-capacity information.
Under the foregoing circumstance, the capacity of the optical disk has been enlarged by providing for a multiplicity of layers for storing information that are laminated in the direction of the thickness of the optical disk.
In such a multilayer optical disk, a multilayer structure is formed on one side thereof and consists of information layers for storing information, wherein the focal points are made so as to be different from one another among the multiple layers so that information is read while maintaining a random access characteristic and, therefore, large-capacity information is handled by a large capacity.
Reported and representative multilayer optical disks will now be described.
1. A concept for reproducing the optical disk by making the positions of the focal points to be different from one another is reported, for example, U.S. Pat. No. 3,946,367.
2. A method using a multilayer disk having an information layer formed by laminating a plurality of layers on one side of the disk so that information is read by means of transmitted light or reflected light is reported, for example, U.S. Pat. No. 4,219,704.
3. A system for reproducing information from a multilayer optical disk, the system comprising an optical system having an aberration correction function (refer to U.S. Pat. No. 5,202,875).
In order to reproduce data in a conventional multilayer optical disk of the foregoing type, an exclusive apparatus for reproducing the data in the optical disk is required. For example, there arises a requirement for a reproducing optical system capable of independently reproducing a reproduction signal from the first information storage layer or the second information storage layer without mixing of data. As an alternative to this, a signal processing system is required which is capable of distinguishing reproduction signals from the first information storage layer and the second information storage layer from each other so as to extract information without confusion.
Therefore, a reproducing apparatus, such as a compact disk player for reproducing a so-called compact disk (CD) which has been used widely as a read-only optical disk, cannot be used as it is.